In conclusion, the efficacies of a triazole fungicide (difenoconazole) for the control of potato early blight (A. The control efficacy of triazole applied following a curative strategy appeared to be closely related to the dose of the applied fungicide. In this study, the control efficacy of triazole applied according to epidemic prediction methods and following a preventive strategy was similar. Therefore, strobilurins may be more efficient than triazole for early blight control. These results were not obtained with triazole fungicide applications whether triazoles were applied preventively, curatively or according to prediction methods. In previous results, preventive sprayings using strobilurin fungicides showed a complete control of early blight symptoms in the field. These results confirmthat fungicide applications based on prediction methods for early blight reduce the number of fungicide applications and provide effective control of potato early blight in comparison to the use of systematic preventive sprayings. In these triáis, the Specware 6.02 system reduced the frequency of fungicide sprays, but it did not reduce the amount of fungicide applied per hectare compared to the standard preventive program based on weekly fungicide applications. A poor efficacy was obtained following curative fungicide programs and the Specware 6.02 disease prediction model when difenoconazole was used at the lowest rate. Preventive fungicide treatments applied at the high rate folowing the Specware 6.02 disease prediction model showed similar efficacy in the control of foliar symptoms and yield. ha -1 of difenoconazole applied according to the Specware 6.02 prediction model overcame the untreated control in potato yields in the 2005 season.None of the fungicide treatments provided complete control of the foliar symptoms of early blight however, they exceeded the untreated control plots in the number of marketable potato tubers produced and in total yield. Under these environmental conditions, fungicide treatments significantly reduced disease severity in comparison to the untreated plots. Data were subjected to analysis of variance, and means from each year were compared using the least-significant difference test (LSD) at p = 0.05.Ĭlimatic conditions were highly favorable for disease development during both growing seasons, implying that maximum disease severity was reached in untreated plants ( Table 1). Each treatment was arranged in a randomized complete block design and replicated four times. Tubers from the two center rows of each plot were harvested and graded into two categories, either marketable (>60 g) or undersize tubers "seeds" (60 g) or undersize tubers "seeds" (<60 g), and the total yield by weight was determined. Disease severity was rated using the 0-50 rating scale (0 = no infection 50 = maximum infection). The same treatments and rates were also applied when the forecast model (Specware 6.02) reached 300 P-Days after emergence, and applications were then repeated thereafter every 7 EAST severity values. ha -1 on a preventive program and on a curative program.Difenoconazole (Bogard 25EC) was sprayed weekly at a rate of 0.25 L Each plot consisted of 4 rows that were 5 meters long. Pampeana PNTA that were susceptible to early blight and resistant to late blight were machine planted in 0.20-m intervals in rows spaced 0.8 mapart. Uncut virus-free seed tubers of potato ( Solanum tuberosum) cv. the 20 growing seasons, two field trials were conducted at the INTA Balcarce Experimental Station (Argentina) to study the control of potato early blight ( Alternaria solani). Casilla 276, 7620 Balcarce, Buenos Aires, Argentina. Control of potato early blight with triazole fungicide using preventive and curative spraying, or a forecasting systemįacultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata y Estación Experimental Agropecuaria, Instituto Nacional de Tecnología Agropecuaria, INTA.
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